Does anyone know what controls flow of hot water into heater core is it some type of valve or door ?

 

There was NO control of coolant flow into the heater core.

 

As was described in u'r other post, there is not a coolant flow controller, the temp. is controlled with a blend door, controlled with the **** on the dash,as you select different temps the door actuates to the selected setting,if u have no control it is usually a bad door( BROKEN), view the video on the "Heatertreater" web sight, as suggested by the previous poster on YOUR first post on this, Subject.